1. Field of the Invention
This invention relates to a gear device composed of a plurality of gears, and particularly to a planetary gear device using non-circular gears.
2. Description of the Prior Art
In factory and office equipment, it often becomes necessary to reduce the rotational velocity of the output shaft of a general purpose 4-pole motor by velocity reduction means and to convert this reduced constant velocity rotation to swing motion, swing rotation, intermittent rotation or some other unconstant velocity rotation. In such a case, it has been the usual practice to interpose unconstant velocity means such as a cam mechanism or a Geneva mechanism. According to such a method, however, it is necessary to provide both velocity reduction means and unconstant velocity means, adding not only to the space for installing the entire device but also to the cost of the device. The use of such a conventional cam mechanism or a Geneva mechanism entails problems such as a limited range of unconstant velocity rotation a high slip factor and low mechanical efficiency.
On the other hand, a planetary gear device has been widely used as a compact device which provides a high reduction gear ratio. Heretofore, circular gears having circular pitch curves have been exclusively used as gears for constituting such a planetary differential gear device. It has also been contemplated to use non-circular gears for constituting a planetary differential gear device, but the use of non-circular gears in that case has been limited to those gears whose teeth can be practically machined, such as elliptical gears. Therefore, even if a planetary gear device fabricated is incorporating elliptical gears, changes in the angular velocity ratio of the angular velocity output relative to the angular velocity input are obtained only in a limited range.
However, recently, with the progress of computers, it has become practicable to design and machine non-circular gears other than elliptical gears (refer to pages 109 et seq. of Precision Machine Society's 1984 Kansai District Regular Scientific Lecture Meeting Theses, and pages 38 et seq. of Second Design Automation Engineering Lecture Theses). Simple use of a set of such non-circular gears, however, fails to produce such motions as intermittent rotation, swing motion, and swing rotation. Thus, it has have been to made in incorporate various non-circular gears in said planetary gear devices for obtaining a unconstant velocity rotational motion useful for automation and to integrate velocity reduction means and unconstant velocity means together (refer to pages 393 et seq., No. 1, Vol. 39, Part 3 of Japan Society of Mechanical Engineers' Theses).
A conventional planetary gear device used in such attempts is schematically shown in FIG. 1. The illustrated planetary gear device comprises an input shaft a rotatably supported in a casing k, a carrier b fixed to the input shaft a, a planetary shaft c eccentrically positioned relative to the input shaft and connected at one end thereof to the carrier b in a cantilever manner, a planetary gear unit d integrally having a main driving gear e and a driven gear f and rotatably supported on the planetary shaft c, an output shaft j rotatably supported in the casing k, an output gear h fixed on the output shaft j and meshing with the driven gear f, and a fixed gear g fixed to the casing k and meshing with the main driving gear e. A pair of non-circular gears are used for each of the combinations of the main driving and fixed gears e and g and the driven and output gears f and h.
The planetary gear device shown in FIG. 1 can be accepted as having integrated velocity reduction means and unconstant velocity means together. On the other hand, since the output shaft j rotates at unconstant velocity while the input shaft a rotates at constant velocity, acceleration acts on the various components on the output side. As a result, the force to be transmitted, i.e. the load, acting between the components on the input side and the components on the output side pulsates. To withstand such a pulsating load, it is necessary, in the planetary gear device shown in FIG. 1, to increase the strength of the various components as compared with a conventional planetary gear device using circular gears. In particular, since the planetary gear unit d integrally has the main driving and driven gears e and f, the axial length increases to a great extent. Since the planetary shaft c supports such planetary gear unit d in a cantilever manner, a bending moment due to the high dynamic load acts on the planetary gear unit c. To withstand such a high bending moment, it is necessary, in the planetary differential gear device shown in FIG. 1, to increase the size of the planetary shaft c, carrier b and input shaft a. Thus, the planetary gear device shown in FIG. 1 inevitably has the drawback that the entire gear device is large-sized and heavy; these drawbacks must be eliminated before the planetary gear device can be put to practical use.